not the same....a euro pulley is lighter; an underdrive pulley is smaller. The underdrive pulley drives the accessories-water pump, alternator etc at less speed so it frees up a horsepower or two. The euro pulley has only one belt groove so it's lighter and thus slightly reduces rotating mass. Like any such reduction in mass, it doesn't really give more horsepower but it lets the motor rev quicker, but in practice you wouldn't be able to tell the difference between a stock pulley and the euro. You probably won't be able to tell the difference from an underdrive pulley either, like I said, it's a very minor difference. Considering the prices people are getting for either one, I think they should be low on your "things to do to go faster" list....for the cost, there are a lot of other things you can do with a much much higher horsepower/cost ratio....